Previous research has shown that administration of dopamine (DA) antagonists in rats results in vacuous jaw movements, which are rapid movements that resemble chewing but are not directed at any particular stimulus. Vacuous jaw movements in rats have many of the characteristics of a parkinsonian tremor. Neuroleptic-induced vacuous jaw movements are reduced by anticholinergic drugs and enhanced by cholinomimetic drugs, as are human parkinsonian symptoms. Recent evidence indicates that vacuous jaw movements in rats are produced by depletion of striatal DA with injections of the neurotoxic agent 6-hydroxydopamine directly into ventrolateral striatum. The proposed experiments are designed to determine if vacuous jaw movements in rats could be used as an animal model of parkinsonian tremor. The first and second experiments will involve a characterization of the oral movements induced by pilocarpine, haloperidol and DA depletion by using videotape analysis and electromyographic recording of jaw muscles. The third experiment will test the effects of anti-parkinsonian drugs on vacuous jaw movements. The fourth experiment will involve the use of microdialysis methods to assess the effects of conditions that produce vacuous jaw movements on ACh release in the ventrolateral striatum. The results of these experiments will indicate if vacuous jaw movements in rats is a model of parkinsonian tremor that could be useful for understanding the pathophysiology of tremor and developing new drugs to treat parkinsonian symptoms.